alpha2-Macroglobulin (alpha2M), a general proteinase inhibitor ubiquitous in the plasma of vertebrates, is believed to serve as a general proteinase scavenger thereby protecting blood and tissue proteins from degradation. A better understanding of the structure- function relationships of human alpha2M will result from the determination of the structure of its various complexes by stain and cryo-electron microscopy, and image processing. The native and transformed molecules (formed upon reaction with a proteinase) are comprised of dimers. The determination of the 3-D structure of the native dimer (protomeric unit) will elucidate the structural organization of the native molecule and offer further insight in the mechanism of proteinase entrapment. The 3-D structure of alpha2M with the truncated bait domain compliments this study since this variant alpha2M is not capable of trapping the proteinase. Bait domain cleavage is the initial step in the reaction Of alpha2M with a proteinase. A 3-D structure of anti-bait domain Fab-labelled native alpha2M will locate this important functional site and make it possible to compare it with the location of this epitope in the transformed structure. Further insight into the mechanism of the transformation of native to the activated structure will be obtained by determining the 3-D structures of monoclonal Fab-labelled native, half-transformed and transformed alpha2Ms. Mammalian pyruvate dehydrogenase complex (PDC) plays a critical role in regulating cellular fuel utilization in the heart and, therefore, studies of the structure-function relationships of the PDC may expand the treatment options for heart disease. Saccharomyces cerevisiae PDC activity is regulated by the pyruvate dehydrogenase component (E1). The 3-D structure (determined by cryo-electron microscopy) of E1 and its binding subunit beta associated with dihydrolipoamide acetyltransferase core complex (E2) will elucidate its disposition on the core and may give insight into its structural organization. The disposition of functional sites associated with the PDC will be elucidated by determining the 3-D structure of these sites labelled with a gold cluster. They include the lipoyl domain of the binding protein (BP) and the catalytic sites of the dihydrolipoamide dehydrogenase (E3). 3-D reconstructions of recombinant intact E2 and the E2 core with BP E3 and E2 BP E3 E1 bound should elucidate the structural organization of this large complex. A 3-D reconstruction of the beef kidney intact PDC will permit a comparison of the mammalian and yeast complexes.